The present invention relates a gas sensor device which detects a particular gas that is introduced into the device. More particularly, the present invention relates to a gas sensor device which may be employed in various equipment used for medical treatment, gas analysis and gas inspection which require accurate and reliable gas detection.
Gas sensors for detecting a given gas introduced therein include those in which a housing accommodating a sensor element is separately assembled to a printed circuit board or the like which constitutes the measuring circuit. For example, the gas sensor requires an assembly step in which, after the sensor element has been soldered to the printed circuit board, the housing is secured to the printed circuit board with screws or the like.
However, such separate assembly of the sensor element and the housing to the printed circuit board or the like involves cumbersome, time-consuming and inefficient assembly operations.
Furthermore, to enhance the accuracy of the sensor, it is necessary to provide a barrier between the space in which the sensor element operates and the external atmosphere. Hence, it is necessary to provide a gas-tight or hermetic seal between the printed circuit board and the housing. Accordingly, the housing must be mounted on the printed circuit board using a packing member such as an O-ring, increasing the number of component parts of the device and rendering assembly even more cumbersome.
Still further depending on the operating situation of the sensor device, there is a risk of hermetic seal deterioration between the printed circuit board and the housing and fluctuation in the volume of space in which the sensor element operates, thereby adversely influencing the sensitivity and accuracy of the sensor.
It is therefore an object of the present invention to provide a gas sensor device having a reduced number of component parts, requiring reduced time for assembly and mounting on a printed circuit board.
It is another object of the present invention to provide a gas sensor device which can reduce irregularities in sensitivity and measurement accuracy.
The above objects of the present invention have been achieved by providing a gas sensor device for detecting the presence of a gas introduced into the device, the device including:
a housing and an inlet and an outlet communicating with the interior of the housing for introducing and discharging said gas to and from the said interior;
a sensor element disposed within said interior for detecting the presence of said gas; and
a base element supporting the sensor element within the interior of said housing, said base element being integrally assembled to said housing.
According to the invention, the base element which supports the sensor element in the housing is integrally assembled to the housing suitably by means of a seal such as a hermetic seal. Such a construction ensures complete segregation between the inside and outside of the housing, and it is unnecessary to separately assemble the housing and the base element to a circuit board or the like. Furthermore, the space in which the sensor element operates is hermetically sealed by the housing and the base element. Thus, no deterioration of the hermetic seal between the housing and the base element and no fluctuation in the volume of the space within the housing can occur, even when inconsistencies occur in the assembly conditions of the housing and base element into the circuit board.
In a first embodiment of the invention, one of the inlet and the outlet is formed by a hollow cylindrical body which extends outwardly from the housing, and the other of the inlet and the outlet is formed by at least one aperture in the housing.
According to this embodiment, the inlet or outlet is formed in a cylindrical shape, and extends outwardly of the housing. Such a construction, for example, enables tubular gas piping to be attached to the inlet or outlet, ensuring that a constant through flow of gas can be achieved in order to guarantee accurate and continuous monitoring.
In a second embodiment of the invention, each of the inlet and the outlet is formed by a hollow cylindrical body.
According to this second embodiment, the inlet and the outlet are provided on the housing at two locations. The inlet serves to introduce the gas into the interior of the housing and the outlet serves to discharge the gas to the outside of the housing. Due to such a construction, a feedback path can be formed to return the gas to its source, avoiding gas wastage.
Preferably, the device also includes a porous body disposed within the interior of the housing intermediate of the inlet and the sensor element.
The provision of the porous body, suitably a filter element, in the path of the gas entering the device through the inlet, ensures that the advancing gas is dispersed by passing through the porous body. This construction prevents the gas from directly impinging on the sensor element, thereby avoiding unnecessary fluctuations in sensitivity and accuracy, for example, caused by cooling of the sensor element.
Suitably, the porous body is sandwiched or clamped between the housing and the base element. This prevents movement of the porous body within the housing while avoiding its direct fixture to either the housing or the base element, for example, with an adhesive.
Suitably, the sensor element is provided with a heat generating component.
The heat generating component enables the sensor element to be self-heating. Such a construction permits use of a sensor element of a type having enhanced sensitivity upon heating or of a type which acts as a detector only upon heating, increasing the utility of the sensor device to a broader range of gases.
Preferably, the sensor element is an oxygen ion conductor enabling it to be used for monitoring the presence and concentration of oxygen in an oxygen-containing gas. It can therefore be used for detecting CO, CO2, NOx or the like, as well as O2 itself, and may be used in medical equipment, diving equipment, gas analyzers, exhaust monitors and the like.